In recent years, speed-sensorless control has been commonly used for induction machines, and position-sensorless control has been commonly used for synchronous machines. For speed-sensorless control, it is important to grasp resistance values of an induction machine or synchronous machine. In particular, the resistance values of a motor (alternating-current rotating machine) vary with temperature. If errors occur between resistance values set by the control side and actual resistance values, desired output torque may fail to be obtained or the electric vehicle may fail to be activated.
As means for solving such a problem, for example, the following Patent Literature 1 describes a method for detecting the applied voltage and the input current to an induction machine for driving an electric vehicle, and estimating a primary resistance and a secondary resistance of the induction machine between when the electric vehicle is activated and when the speed of the electric vehicle is in a low speed range. The following Patent Literature 2 describes a method for temporarily applying a direct-current voltage or pulsating voltage to an induction machine for a certain period immediately after an operation command rises from zero, and estimating the primary resistance and secondary resistance of the induction machine.